Method of recovering tin from scraps of tinned iron.



No. 736,924. PATBNTED AUG. 25, 1903.

B. A. BERGMAN.

METHOD OF REGOVERING TIN FROM SGRAPS OP TINNED IRON. APPLIOATIQN FILED JAN. 15. 1902.

N0 MODEL.

r r-r r w vbvwoeo Suva/who;

' @zM Z/i mowin BROR AXEL BERGMAN,

I Patented'August 25, 1903;

PATENT Fr es.

or NYFORS, SWEDEN.

srEcmoArIoN forming part of letters Patent No. 736,924, dated August at, race.

Serial No. 89,860. (in specimens.)

To all whom it may concern: Be it known that I, BROR AXEL Bananas, mechanical engineer, of Nyfors, Eskilstuna, Sweden, do hereby declare the nature of my invention for an Improved Method of RecoveringTin from Scraps of Tinned Iron and in what manner the same is to be performed to be particularly described and ascertained in and by the following statement and the accompanyingdrawing, showing a vertical section of a form of apparatus that inay be used.

The electrolytic processes hitherto employed for recovering tinfrom scraps of tinned sheet-iron are all based on introducing the scraps, either compressed or contained in baskets, as the anode into an acid or alkaline electrolyte and by means of an electric current dissolving the tin and depositing it on the cathode. The disadvantage connected with all these processes lies in the electrolytes soon becoming useless and requiring renewal the acid-baths, owing to dissolution of iron, which causes high tensions accompanied by greater difliculty of dissolving the tin and the depositions of an impure product on the cathode, since basic salts are deposited and iron is also precipitated when the current density increases; the alkaline electrolytes, owing to an increase of stannate of alkali in solution, probably depending on the tin being dissolved as divalent iron, but separated as a tetravalent one, so that the same quantity of electricity dissolves more tin at the anode than is precipitated at'the cathode, to this being added the action of the carbonic acid of the air in forming carbonate of alkali, which is likewise useless for the solution of the tin. When the percentage of stannate and carbonate of alkali is increased and that of caustic alkali decreased, the tension of the bath rises, oxygen and hydrogen are generated, the tin dissolves with greater diificulty, and the scrap-iron being but imperfectly freed from tin becomes useless for smelting into high-grade iron, the electrolyte,moreover,becoming worthless and must be replaced and subsequently regenerated in some suitable manner. Briefly speaking, by anodic dissolution and cathodic precipitation it is impossible whether withacid or alkaline electrolytes to work any length of tiine, the pointbeing soon reached where the and interfering with the process.

from'outside source had to be applied. and the troubles already mentioned were encounte l'( 1 l. The consequence has been that at the present state of the art the detinnedscra p-iron is contaminated withsome tin and fetching only a i very low price in the market.

Thepresent electrolytic process for recovering tin from scraps of tinned iron, and which is thesubjecti'of this application, is based on an entirely diiferent principle. Accordin g to this method, to be sure, tin is dissolved by means of caustic alkali, though in such manner that a primary battery form ed for transforming the chemical energy developed into electric energy, and the action is strong enough to dissolve every particle of tin. In other words, I have succeeded in arranging the apparatus in such a way that the electric energy generated is neither too weak nor too strong. .I do this byintroducing adcpolarizing compound into the galvanic pair. I am well aware that depolarizers have long-been used in connection with galvanic pairs for the purpose of generating electricity, but I have discovered the great beneficial action of using a depolarizer in connection with detinning tin-scrap in a caustic solution. The electric energy generated in this manner when the tin is dissolved into stanuate of alkali taken upby and stored in storage batteries connected with the poles of the apparatus in such a manner that the said energy may be used in the final precipitation of the tin or for any other purpose.

Thus A is an iron tank filled with a solution of caustic.

B is a basket suspended in the tank and resting on the insulating-blocks C.

5 to the tin, which is oxidized and combines with the alkali into stannate of alkali. ()n the discontinuance of the action of the primary battery-i. (2., when the solution of alkali has become saturated with stannate of IO alka1i-the solution is drawn OE and treated bywell-known processes for recovery of tin in commercial form. The oxid of copper used as depolarizer and reduced in an early stage of the process into finely-divided metallic'cop- 5 per may be readily regenerated by glowing in a current of air.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is- An improved method of recovering tin from scrap of tinned iron which consists in providing a solution of caustic alkali containing a depolarizer, in placing said scrap as a negative pole and a metal electropositive to the same as a positive pole in contact with said solution, permitting the tin to dissolve into stannate of the alkali, and to generate a current, and finally recovering the tin, substantially as described.

In witness whereof I have hereunto set my hand in presence of two witnesses.

BROR AXEL BERGMAN.

Vitnesses: H. TELANDER, T. RISBERG. 

